Adults are often brightly coloured, with red or orange males and green or yellow females, but there is wide variation in colour, beak size and shape, and call types, leading to different classifications of variants, some of which have been named as subspecies. Crossbills are characterized by the mandibles crossing at their tips, which gives the group its English name.
Crossbills are specialist feeders on conifer cones, and the unusual bill shape is an adaptation which enables them to extract seeds from cones. Using their crossed mandibles for leverage, crossbills are able to efficiently separate the scales of conifer cones and extract the seeds on which they feed.
The Red Crossbill breeds in the spruce forests of North America, as well as Europe and Asia. Some populations breed in pine forests in certain areas of all three continents, and in North America, also in Douglas-fir. It nests in conifers, laying 3-5 eggs. Mediaeval sketch by Matthew Paris in his Chronica Majora (1251) of a Crossbill holding a fruit in its beak, with the Latin words Alaudis parum majores ('a little bigger than Larks'). This crossbill is mainly resident, but often irrupts south when its food source fails. This species forms flocks outside the breeding season, often mixed with other crossbills.